This invention relates to a method for manufacturing extrusion molded silicone insulating articles.
As is well known in the art, silicone rubbers are widely used in a variety of applications because of their improved heat resistance, low-temperature resistance, and electrical properties.
In particular, silicone rubbers are advantageously used in an extrusion molded form as electric conductor insulating coatings, insulating tubes, anode caps, and other articles which are required to have high electrical insulation. Depending on the intended application, the silicone rubber composition is often modified to increase the dielectric strength as by increasing the density, increasing the rate of vulcanization, increasing the degree of crosslinking, sufficiently deaerating, reducing the content of volatile matter, and reducing the content of electrical impurities.
However, such modifications can merely improve the dielectric strength of silicone rubbers to the range of about 20 to 30 kilovolts/mm on average, which range is not regarded as being satisfactory. With such a degree of electrical insulation, silicone rubber compositions must be extrusion molded to a substantial thickness when it is desired to use the extrusion molded compositions in such applications as conductor insulation. For this and other reasons, conventional silicone rubber compositions are inconveniently used to produce insulating articles capable of meeting the current requirements of compactness and light weight. Increased thickness requires vulcanizing conditions which includes vulcanizing rate and heat consumption which are disadvantageous for commercial manufacture.